Study: Fish Oil Pills Don’t Stall Alzheimer’s

There was good reason to believe that fish oil, which has been linked to health benefits for the heart, might also work its medical magic on the brain, particularly with Alzheimer’s disease. Preliminary studies hinted that people with higher levels of fish oil in their blood were less likely to develop Alzheimer’s, while animal experiments also supported a strong beneficial link.

But a study led by Dr. Joseph Quinn, a neurologist at Oregon Health and Science University, calls that assumption into question. In a study involving nearly 300 volunteers, some of whom and Alzheimer’s and others who served as controls at 51 research sites in the U.S., Quinn and his team found that fish oil supplements did not improve cognitive scores on a mental test among those taking 2 g daily during the study’s 18 months. (More on Time.com: Photos: My Aging Father’s Decline: A Son’s Photo Journal)

While he wasn’t expecting a dramatic change, Quinn had hoped, based on the animal and smaller human studies, that the docosahexaenoic acid (DHA) found in fish oil would confer some benefit in improving dementia symptoms. “The results did disappoint me,” he admits. “I really thought we were going to have a modest effect on the rate of progression of the disease, and the fact that we didn’t see any effect was definitely disappointing. But Alzheimer’s is a tough nut to crack.”

For one, he says, it may simply be that the fish oil supplements were started too late to have any effect on the already established disease process. Alzheimer’s is characterized by the buildup of amyloid protein in the brain, which triggers a cascade of events that leads to the death of nerve cells critical for memory, learning and intellectual functioning. By the time patients show symptoms of memory loss and dementia, the amyloid deposits are well entrenched, making any effect DHA may have moot. (More on Time.com:Cover Story: Alzheimer’s Unlocked)

It’s also not clear exactly how DHA might be affecting progression of the disease in the animal models, so Quinn says that better knowledge of that process might help to make DHA more effective in controlling symptoms in human patients. Is DHA effective in preventing cells from generating amyloid in the first place, or is it more powerful in clearing deposits of the protein once it begins to pile up? Since Quinn’s trial was completed, new studies suggest that DHA may work as a clearing agent; so far scientists have only investigated this effect in animal models and human cell cultures, but Quinn is hoping to study the mechanism in patients soon.